Old NTL cancellation problem?

[selkie]

Just for 'fun', I've discovered today that an NTL Freedom account I'd cancelled in October 2005 was not cancelled, they have no record of the request to cancel it, and despite proof that they had my new address (they sent a small credit refund there!), they claim I owe money that they sent no bills nor requests for. I'm attempting to write up a letter complaining/disputing, and make copies of *everything*, right now. Luckily, I keep every bit of paper I'm sent.

For added fun, all of my documentation has the same account number, covering both regular service at one address (complete with disconnect notice), and NTL Freedom at a second address. This makes me worry now that they've messed up the mailing, billing, or account numbers, and that maybe it was all meant to cover the first regular service account; that would mean that I never got anything whatsoever related to the NTL Freedom account, so I'd have no proof of anything and of course I wouldn't have been able to pay correctly. On the other hand, direct debit which they admit to receiving for the NTL Freedom account was also under the same account number, so maybe just the one account number is correct. Is there any way to check?

My main question is, is there any advice for dealing with this? My stance is that I requested the account be closed (because I was moving to a new address where service was not offered) and they failed to close it or even make a record of that; they then failed to inform me of, well, anything. No notices, and the only further bills all show a small credit - up until it's refunded, and then there are no further bills either. I'd like to ask them for written confirmation that my account, or accounts, are now closed; I'm also asking that any charges after the time I *tried* to cancel the accounts be removed.

What documentation will I need to include? Is there any set policy for disputing charges that I can refer to? Is there any advice for making the letter as effective as possible?